I have observed that insulating supports for helically wound fusible elements made of laminates of glass cloth and synthetic resins, particularly melamine resins, perform very differently depending upon the current-carrying capacity of the fusible element and depending upon the area of the interface between the fusible element and the support. In fuses having a very small current rating, wherein the fusible element is in the form of a thin wire, and the interface between the fusible element and a support for it of an organic substance as, e.g. melamine, are very small, such supports performed perfectly. As the current-carrying capacity of the fusible element is increased, and with the transition from one to a plurality of narrowly spaced fusible elements, with the substitution of wire-like fusible elements by ribbon-type fusible elements, and with the concomitant increase of the interface between the fusible elements and their organic supports, the quality of the performance of the latter decreases. It thus appears that laminates of glass cloth and synthetic resins may be used as supports for the fusible element or elements up to a certain point, beyond which point the performance of such supports becomes unacceptable.
It is, therefore, one object of this invention to provide electric fuses with helically wound fusible elements having supports therefor which are of a laminate of glass cloth and a synthetic resin and which supports perform satisfactorily in the absence of ceramic materials for supporting the fusible element, even under conditions where supports of glass cloth and synthetic resin would normally fail.
Another object of this invention is to avoid ceramic materials, and in particular high alumina content materials, for supporting helically wound fusible elements because such materials are much more expensive than laminates of glass cloth and synthetic resins, and because such materials are extremely difficult to form.